Response

Once fetch method is called, Eden Treaty return an Promise with object as follows:

data - returned value of the response (2xx)
error - returnd value from the response (>= 3xx)
response Response - Web Standard Response class
status number - HTTP status code
headers FetchRequestInit['headers'] - response's headers

Once returned, you must provide an error handling to ensure that value is truly returned to access the value, otherwise the value will be nullable.

typescript

import { Elysia, t } from 'elysia'
import { treaty } from '@elysiajs/eden'

const app = new Elysia()
    .post('/user', ({ body: { name }, error }) => {
        if(name === 'Otto')
            return error(400, 'Bad Request')

        return name
    }, {
        body: t.Object({
            name: t.String()
        })
    })
    .listen(3000)

const api = treaty<typeof app>('localhost:3000')

const submit = (name: string) => {
    const { data, error } = await api.user.post({
        name
    })

    // type: string | null
    console.log(data)

    if(error)
        switch(error.status) {
            case 400:
                // Error type will be narrow down
                throw error.value

            default:
                throw error.value
        }

    // Once error is handle, type will be unwrapped
    // type: string
    return data
}

import { Elysia, t } from 'elysia'
import { treaty } from '@elysiajs/eden'

const app = new Elysia()
    .post('/user', ({ body: { name }, error }) => {
        if(name === 'Otto')
            return error(400, 'Bad Request')

        return name
    }, {
        body: t.Object({
            name: t.String()
        })
    })
    .listen(3000)

const api = treaty<typeof app>('localhost:3000')

const submit = (name: string) => {
    const { data, error } = await api.user.post({
        name
    })

    // type: string | null
    console.log(data)

    if(error)
        switch(error.status) {
            case 400:
                // Error type will be narrow down
                throw error.value

            default:
                throw error.value
        }

    // Once error is handle, type will be unwrapped
    // type: string
    return data
}

By default, Elysia will infers error and response type to TypeScript automatically, and Eden will be providing an auto-completion and type narrowing for accurate behavior.

TIP

If server response with HTTP status >= 300, then value will be always be null, and error will have a returned value instead.

Otherwise, response will be passed to data.

Response ​

Response